1. Field of the Invention
The present invention relates to an exhaust gas purifying catalyst suitable for application to processing for purifying exhaust gas discharged from an internal combustion engine, and relates to a producing method thereof.
2. Description of the Related Art
In recent years, in order to remove toxic substances such as a hydrocarbon compound (HC), a carbon monoxide (CO) and a nitrogen oxide (NOx), which are contained in exhaust gas discharged from an internal combustion engine, an exhaust gas purifying catalyst has been widely used, in which noble metal particles of platinum (Pt) and the like are supported on a metal oxide support of alumina (Al2O3) or the like. In the conventional exhaust gas purifying catalyst, in order to enhance durability of the noble metal particles against variations of the ambient atmosphere, a large amount of the noble metal particles are used. However, it is not desirable to use the large amount of noble metal particles from a viewpoint of protecting earth resources.
From such a background, recently, attempts have been made, which are to enhance the durability of the noble metal particles in such a manner that transition metal such as cerium (Ce) and manganese (Mn) or a transition metal compound, which functions as an oxygen storage component (OSC) material, is disposed in the vicinities of the noble metal particles by an impregnation method, and the variations of the ambient atmosphere of the noble metal particles are suppressed by the transition metal or the transition metal compound (refer to Japanese Patent Laid-Open Publications No. H8-131830 (published in 1996), No. 2005-000829, No. 2005-000830 and No. 2003-117393). Note that, in accordance with such a method, enhancement of activity of the noble metal particles can also be expected in addition to the enhancement of the durability of the noble metal particles.